3 Oct 2026
Patient history
A 28-year-old woman presents with four days of severe, colicky, generalised abdominal pain and vomiting. This is her third such admission in two years; laparoscopy last year found nothing. She started a new medication three weeks ago.
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Acute intermittent porphyria
Intravenous hemin with carbohydrate loading
The pain is real and the abdomen is not its source. That is the paradox of an acute porphyric attack: severe colicky pain over a soft, non-tender abdomen with normal inflammatory markers and normal imaging, because the pain is neuropathic, arising from autonomic nerve dysfunction rather than from anything inside the abdomen. It is why last year's laparoscopy found nothing, and why a fourth negative scan would settle nothing either. Add a motor-predominant peripheral neuropathy, psychiatric disturbance, tachycardia and hypertension from autonomic instability, and the pattern becomes distinctive. The hyponatremia is genuine SIADH, confirmed by a low serum osmolality with inappropriately concentrated urine and high urine sodium; it is a common feature and can precipitate seizures. Urine darkening on standing in light reflects porphobilinogen oxidising to porphobilin, which is why samples must be protected from light and sent fresh. A markedly raised urine porphobilinogen with normal faecal porphyrins localises the defect to acute intermittent porphyria rather than variegate porphyria or hereditary coproporphyria. The recently started medication is almost certainly the precipitant: enzyme-inducing drugs increase haem demand and drive ALA synthase, and the classic culprits include many anticonvulsants, sulfonamides, rifampicin and the combined oral contraceptive. Treatment attacks the same pathway from the other end. Intravenous hemin suppresses ALA synthase by negative feedback and shuts off production of the toxic precursors, shortening the attack and preventing the neuropathy from progressing; high-dose carbohydrate does the same thing far less effectively and is started at once while the hemin is being sourced. Withdrawing every precipitant matters as much as either: the new drug, alcohol, and any period of fasting. The sodium of 119 mmol/L is the trap in the management rather than the diagnosis: it brings a real seizure risk, and most anticonvulsants are themselves porphyrinogenic, so the hyponatremia must be corrected rather than treated around.